1. Field of the Invention
The invention relates to the field of brachytherapy. In particular the invention relates to an expandable brachytherapy device and methods of using it with the ability to provide a tailored radioactive dose profile.
2. Description of the Related Technology
A variety of devices exist for performing brachytherapy on the body. Exemplary devices that are employed in body cavities or cavities created in the body by surgery include, for example, brachytherapy devices for treatment of breast cancer, uterine cancer, prostate cancer, treatment of a cavity left by removal of a tumor, cyst, polyp or similar mass, and treatment or prevention of restenosis. Some of these devices are merely implants that are implanted in a cavity in the body to deliver the treatment. However, certain types of devices are expandable to allow insertion of the device into the body in an unexpanded state, and subsequent expansion of the device to deliver the brachytherapy. Such expandable devices are particularly useful for the treatment of, for example, breast cancer, vascular restenosis and uterine cancer.
Breast cancer affects many women. Not only is breast cancer a serious and life threatening illness, quite frequently the methods involved in treating breast cancer can have dramatic life altering cosmetic ramifications for a woman. Treatments, such as mastectomies, involve radical surgical procedures that while saving a patient's life, oftentimes extract a high price on both the physical and mental health of a patient. Other treatment methods may be preferable because of these drawbacks.
One method of treating breast cancer is by subjecting a cancerous tumor to radiation treatment. Although, doing this can be as effective in curing breast cancer as more radical procedures, there is a chance that the intense radiation used in destroying the cancer can adversely affect healthy tissue in the area surrounding the area treated. One method for avoiding potential damage to healthy tissue is through the use of special brachytherapy treatment procedures. Applying radiation treatment according to a specialized treatment plan may permit a more effective treatment while minimizing undesirable consequences of that treatment.
In a patient with breast cancer one method of treating the cancer is to excise the tumor without removal of the entire breast. Excising the tumor is performed in a procedure called a lumpectomy. A lumpectomy is the surgical removal of a tumor in the breast, along with a small margin of the surrounding normal breast tissue. A lumpectomy may also be called a wide excision biopsy, breast conserving therapy or quadrantectomy (this latter term is used when up to one fourth of the breast is removed). The procedure is often performed on women with small or localized breast cancers and can be an attractive surgical treatment option for breast cancer because it allows women to maintain most of their breast after surgery. Several studies have shown that women with small breast tumors have an equal chance of surviving breast cancer regardless of whether they have a lumpectomy, followed by a full course of radiation therapy, or mastectomy (complete breast removal, which generally does not require post-operative radiation treatment). A lumpectomy may be performed using a local anesthetic, sedation, or general anesthesia, depending on the extent of the surgery needed. The surgeon makes a small incision over or near the breast tumor and excises the lump or abnormality along with a margin of an appropriate thickness of normal surrounding breast tissue.
Upon excision of the tumor, a cavity is created in the space where the tumor once existed, however some cancerous tissue may remain at the margins. In order to ensure a full recovery, radiation therapy is applied in the area where the tumor was located. An exemplary method for performing radiation therapy is to employ an expandable brachytherapy device that has been inserted into the cavity that remains after the lumpectomy.
One method for using brachytherapy to treat breast cancer involves placing a radioactive source within a balloon catheter that has been inserted into the cavity formed by the lumpectomy. The radioactive source is placed within the central lumen of the balloon catheter, which is generally centered on the longitudinal axis of the expanded device. This practice places significant limitations on the ability to customize the treatment for a particular patient. For example, placing the radioactive source within the central lumen of the balloon does not permit the radioactive dosage to be tailored to treat primarily only the areas surrounding the cavity that require irradiation. Also, placement of the radioactive source in the central lumen may result in healthy tissue being exposed to undesirable amounts of radiation during exposure of the tissue requiring treatment and/or underexposure of tissue that is a high risk for cancer recurrence. This is at least partially due to the fact that the cavity created by the lumpectomy is generally non-uniform in shape, thereby creating a situation where the distance from the central lumen to tissue at the edge of the cavity may vary at different locations in the cavity, or healthy tissue is located in the treatment region of the radiation field. This is also partially due to the fact that healthy tissue may be located closer to the central lumen at some locations than at other locations. This means that in the interest of preserving healthy tissue and minimizing dose to the skin, the physician may have to use a dose distribution that is less effective than desired. Alternatively, should the physician employ a dose sufficient to ensure effective treatment, healthy tissue may be damaged. As a result, many physicians opt for alternative treatments to avoid the risks associated with the prior art devices.
The catheter material must be stiff enough to maintain structural and functional integrity and flexible enough to minimize discomfort and the chance of injury. A broad range of technical properties (modulus of elasticity, apparent flexural modulus, and durometer) can be achieved by using variations on the thousands of different resins that are current commercially available. The catheters are typically constructed of many different materials such as: polyvinyl chloride (PVC), polyethylene (PE), polyolefin copolymer (POC), nitinol, fluoropolymers, polyurethane (PU), polyetheretherketone (PEEK), polyimide, polyethylene terephthalate (PET), super-elastics, and shape memory materials. The materials used may also be rendered radio-opaque by the loading of additives such as barium sulfate.
Some prior art brachytherapy methods using balloon catheters to deliver the radioactive source are discussed below.
An article by Paul V. Harper from 1966, entitled “Some Therapeutic Applications of Radioisotopes,” published in the Journal MSMA, discusses use of balloon catheters for the treatment of cancer. Harper describes a water filled balloon provided with a central glass tube which can be used to fill the balloon. A radioactive tantalum wire is inserted into the central glass tube once the balloon is located at the treatment area and inflated in order to provide brachytherapy to the treatment area. The Harper device provides an isodose curve that is substantially the same shape as the inflated balloon surface of the device. Harper also describes filling a specially-designed catheter with a liquid solution of radioisotope after the catheter has been inserted into the body in order to provide radiation to the treatment area. In addition, Harper describes the provision of plastic spheroids coated with a radioactive material, which may be packed into a cavity in the body for delivery of a brachytherapy treatment.
Another method for interstitial brachytherapy involves the insertion of a plurality of hollow needles or catheters into the breast and through the surgical cavity in the breast, followed by placement of radioactive sources in the needles according to a predetermined treatment plan. High dose rate iridium sources as well as seed strands are examples of the type of radiation sources that may be employed in this type of interstitial brachytherapy.
U.S. Pat. No. 6,482,142 to Winkler et al. discloses a catheter for use in a method for interstitial brachytherapy in a tumor bed. Winkler discloses a device, shown in FIG. 4, having a radiation source 82 made of three wires 84, 86, and 88, each having a plurality of radiation particles. Wire 86 is a straight wire that extends along the axis of the device and wires 84 and 88 are curved wires that may be made from a shape memory material to allow deformation of the wires for insertion and removal from the catheter. More or fewer wires can be provided.
U.S. Pat. No. 5,302,168 to Hess discloses using a balloon catheter for the treatment of restenosis. FIGS. 2-4 show a balloon 36 with radioactive elements 38 attached to the outer surface thereof. Alternatively, the surface of the balloon may be coated with radioactive material. It appears from FIG. 4, that the radioactive elements 38 expand from a first size, shown in FIG. 2, to a second, larger size, shown in FIG. 4, as the balloon 36 expands.
U.S. Pat. No. 5,863,284 to Klein discloses a balloon catheter for use in angioplasty. Radioactive sources 30 are spaced around the circumference of the balloon. The sources may be attached to the balloon (FIGS. 4 and 4a) or may be contained in a sleeve 48 designed to fit over the balloon (FIGS. 9-10). At col. 13, lines 1-30, a distal portion 18 includes a plurality of slits to allow expansion of distal portion 18 when the balloon is inflated to thereby position radioactive elements 30 at substantially uniform intervals around the inflated balloon. At col. 14, lines 46+, a device is described wherein the distal portion 18 includes an elastomeric expansible region 38 which allows expansion of the distal portion 18 when the balloon is expanded to maintain equal spacing of the radioactive elements about the circumference of the balloon. In the embodiment of FIGS. 7-8 described at col. 15, lines 5-19, the distal portion 18 includes a plurality of folds which allow expansion of the distal portion when the balloon is inflated. At col. 15, lines 20-25, the embodiment shown in FIGS. 9-10 is described. In this embodiment, a sleeve 48 containing a plurality of folds is fitted over the balloon. The sleeve 48 is expandable by virtue of the folds when the balloon is expanded. In yet another embodiment, the radioactive element is integrally formed with the balloon such that the radioactive element moves with the balloon as the balloon is expanded. To improve the uniformity of the radiation dose, the device may employ a secondary radiation source in the form of a guide wire inserted into the central lumen of the balloon catheter.
The devices discussed above offer various methods for using a balloon catheter in brachytherapy, but do not address the provision of customized dosing which can be achieved through the use of certain advantageous features of the present invention discussed below and set out in detail in the detailed description of the preferred embodiments. It is an object of certain embodiments of the invention to provide an apparatus and method for providing tailored brachytherapy treatment.